Many industrial processes produce waste heat of low temperature, typically less than 150° C., which is typically too low to be used to accomplish useful work. Certain thermodynamic cycles, such as absorption refrigeration, can provide environmental cooling from low grade heat sources. Similarly, solar thermal energy received in a solar collector such as a concentrating type or an evacuated tube type is typically of the order of waste heat, and has been employed in absorption chillers to provide environmental cooling. Unfortunately, the absorption refrigeration cycles typically used suffer from inefficiency, and are typically unable to achieve a thermal coefficient of performance (COP) greater than about 0.7, where the term COP is defined as ΔQcold/ΔQin, where ΔQcold is defined as the change in heat of the load and ΔQin is defined as the heat consumed by the cooling system. In vapor compression air conditioning, the COP is defined as ΔQcold/ΔW, and is typically in the order of 3-3.5, where ΔQcold is defined as above and ΔW is defined as the electrical work consumed by the cooling system. Furthermore, current state of the art waste heat driven A/C systems, such as absorption chillers utilizing the absorption refrigeration cycle, are incapable of operating in the absence of sufficient waste heat, and therefore require a complete additional system for backup.
U.S. Pat. No. 6,581,384 issued Jun. 24, 2003 to Benson, the entire contents of which is incorporated herein by reference is addressed to a process and apparatus for utilizing waste heat to power a reconfigurable thermodynamic cycle that can be used to selectively cool or heat an environmentally controlled space, such as a room or a building. Disadvantageously, the system of Benson requires, inter alia, a five way valve which adds to cost and complexity. Furthermore, the system of Benson exhibits a low overall COP, is incapable of operating in the absence of waste heat on residual power and is operative at temperatures of about 200° C., (400° F.) which increases cost.
What is desired is a method and system for providing air conditioning from waste heat which exhibits an improved overall coefficient of performance, preferably with the capacity to further provide backup heating and cooling when the waste heat source is unavailable